1. Field of the Invention
The present invention relates to an apparatus and method for opening bags used in a bag filling and packaging machine. More particularly, the present invention relates to a bag opening apparatus and method for use in a bag filling and packaging machine using flat bags as packaging bags. It should be noted that the term xe2x80x9cflat bagsxe2x80x9d as used herein includes the type that has a chuck at the bag mouth portion.
2. Discussion of Related Art
There is a conventional bag filling and packaging machine of the type in which an operation of opening a bag and an operation of filling the bag with a material to be packed are carried out at the same step. With this type of packaging machine, however, the processing time at each step becomes undesirably long. Therefore, the operating speed of the packaging machine cannot be increased. To cope with this problem, one type of conventional bag filling and packaging machine adopts a method wherein a bag opening step and a filling step are carried out separately from each other. That is, a bag is opened at the bag opening step, and the bag thus opened is moved to the filling step to fill it with a material to be packed.
With the above-described method, however, some problems may arise when flat bags are used. That is, the mouth of a flat bag is opened by pulling the bag from both sides using suction cups, for example, and in this state, air is sent into the bag from the mouth to open the bag as far as the bottom thereof. The bag thus opened may be undesirably closed during movement to the subsequent step, i.e. filling step, by the action of air resistance applied to the bag during the movement, or by the bag""s own restoring force or the like. A bag undesirably closed in this way may interfere with the filling operation.
To solve the above-described problem, Japanese Pat. No. 2981952 discloses an apparatus having a driving arm adapted to reciprocate between a bag opening step and a filling step. The apparatus further has an opening and closing arm secured to the driving arm and a mouth opening claw attached to the opening and closing arm. The opening and closing arm and the mouth opening claw are opened and closed by using a cam and a cam follower. At the bag opening step, the driving arm is moved downward to insert the closed mouth opening claw into a bag having its mouth opened with suction cups. When the bag is moved to the filling step, the cam follower separates from the cam, thereby expanding the opening and closing arm to open the bag as far as the bottom thereof. In this state, the driving arm is moved to the filling step, together with the bag. After a filling hopper has been inserted into the mouth of the bag, the driving arm is moved upward so as to be removed from the bag. Thereafter, the driving arm is returned to the bag opening step, and the cam follower is brought into abutting contact with the cam to close the mouth opening claw.
With the arrangement of the above-described apparatus, the bag is transferred from the bag opening step to the filling step while being maintained in the open state by the mouth opening claw. Therefore, the problem that the bag is undesirably closed will not occur.
However, in the bag opening apparatus that moves in such a manner as to follow the movement of the bag from the bag opening step to the filling step, it is necessary to return the driving arm from the filling step to the bag opening step in order to open the subsequent bag. Therefore, the apparatus requires time for returning the driving arm. This limits the achievement of an increase in the operating speed of the packaging machine. Further, the apparatus itself becomes complicated and costly. In addition, the operating efficiency lowers in maintenance or a cleaning operation.
The present invention was made in view of the above-described problems associated with the prior art.
Accordingly, an object of the present invention is to provide a bag opening apparatus and method for flat bags that is capable of moving a bag opened at a bag opening step to a filling step while surely maintaining the bag in the state of being open and also capable of attaining an increase in the operating speed of packaging machines.
Another object of the present invention is to provide a bag opening apparatus and method for flat bags that is simple in arrangement and capable of being provided at low costs and that is excellent in operating efficiency in maintenance and so forth.
To attain the above-described problems, the present invention provides a bag opening apparatus including a mouth opening device for opening a mouth portion of a bag. The apparatus further includes a bag bottom deforming device for deforming at least a part of the bottom of the bag inward of the bag whose mouth portion has been opened by the mouth opening device. Further, the apparatus includes a bag movement restraining device for restraining movement of a portion of the bag in the vicinity of the bottom thereof, particularly the movement of that portion in a direction approximately perpendicular to a planar portion of the bag, so that the movement is restricted within predetermined limits.
The bag bottom deforming device may include an abutting member for abutting on the bottom of the bag to deform the bottom inward of the bag and an elevating-and-lowering device for vertically moving the abutting member. More specifically, the abutting member may be a rod-shaped member. The abutting member is brought into abutting contact with the bottom of the bag at an approximately central portion in the width direction of the bag and moved upward by the elevating-and-lowering device to deform the bottom of the bag.
More specifically, the bag movement restraining device may be formed from retaining plates disposed at both sides of the bag so as to face each other across the bag. The retaining plates are capable of moving toward and away from each other. The retaining plates have bag movement restraining portions arranged such that when the retaining plates move toward each other, the bag movement restraining portions face each other across each side edge portion of the bag over a predetermined height range from the bottom of the bag.
In addition, the present invention provides a bag opening method including the step of opening the mouth of a bag and the step of deforming the bottom of the bag inward of the bag. The method may further include the step of restraining a portion of the bag in the vicinity of the bottom thereof from moving in a direction approximately perpendicular to a planar portion of the bag when the bottom of the bag is deformed.